GLP-1 receptor agonists — semaglutide (Ozempic, Wegovy), tirzepatide (Mounjaro, Zepbound), and liraglutide (Saxenda) — have transformed the treatment of obesity and type 2 diabetes. Millions of people are now using these medications, and for many, the results are dramatic.

But starting a GLP-1 medication without baseline lab work is like driving without a dashboard. You won't know what's changing, what's improving, or if something is going wrong.

Whether you're about to start, already on a GLP-1, or managing your own protocol through a telehealth provider, here are the blood tests that matter — and why.

These tests establish your starting point. They're essential for measuring progress, catching contraindications, and protecting your health during treatment.

HbA1c reflects your average blood sugar over the past 2–3 months. It's the primary marker for diagnosing and monitoring type 2 diabetes and prediabetes.

GLP-1 medications were originally developed as diabetes drugs — they work by stimulating insulin release and suppressing glucagon. Even if you're using a GLP-1 purely for weight loss, knowing your baseline A1c tells you:

• Whether you have undiagnosed prediabetes or diabetes
• How much your blood sugar control improves over time
• Whether your dose may need adjustment

Normal: Below 5.7% | Prediabetes: 5.7–6.4% | Diabetes: 6.5% and above

Fasting glucose gives a snapshot of your blood sugar after an overnight fast. Fasting insulin tells you how hard your pancreas is working to keep that glucose in range.

High fasting insulin with normal glucose is a hallmark of insulin resistance — the metabolic state that precedes type 2 diabetes and is strongly associated with obesity, PCOS, and cardiovascular disease. GLP-1 medications directly address insulin resistance, so this baseline is valuable for measuring improvement.

The CMP covers kidney function (creatinine, BUN, eGFR), liver function (ALT, AST, alkaline phosphatase), electrolytes, and blood glucose. It's a broad safety screen that's important for several reasons:

• Kidney function: GLP-1 medications can affect kidney function, particularly in people with pre-existing kidney disease. Baseline creatinine and eGFR are essential.
• Liver function: Non-alcoholic fatty liver disease (NAFLD) is common in people with obesity and insulin resistance. GLP-1 medications often improve liver fat — having a baseline lets you track this.
• Electrolytes: Nausea and reduced food intake (common side effects) can affect electrolyte balance.

GLP-1 medications consistently improve lipid profiles — reducing triglycerides, lowering LDL, and raising HDL. But you need a baseline to see how much improvement you're getting.

A full lipid panel includes total cholesterol, LDL, HDL, and triglycerides. If your provider orders it, a non-HDL cholesterol and LDL particle size can add further detail.

A CBC checks red blood cells, white blood cells, and platelets. It's a general health screen that establishes your baseline and can flag anemia (common in people with poor nutrition) or other issues before you begin a protocol that may significantly change your eating patterns.

This one is often overlooked but important. Hypothyroidism causes weight gain, fatigue, and metabolic slowdown — symptoms that overlap with the conditions GLP-1 medications treat. If your thyroid is underactive, you may not respond as well to GLP-1 therapy, and the underlying issue will go unaddressed.

Additionally, there is a theoretical concern (based on animal studies) about GLP-1 medications and thyroid C-cell tumors. While this has not been demonstrated in humans, people with a personal or family history of medullary thyroid carcinoma (MTC) or MEN2 syndrome should not use GLP-1 medications. A baseline TSH and discussion with your provider is appropriate.

Rapid weight loss — which GLP-1 medications can produce — is a known trigger for gout flares in people with elevated uric acid. If you have a history of gout or suspect elevated uric acid, a baseline test before starting is worthwhile.

Once you're on a GLP-1 medication, regular monitoring helps you track progress, catch side effects early, and optimize your protocol.

HbA1c — The most important progress marker. Most people see meaningful improvement within 3–6 months. If you're using a GLP-1 for diabetes management, your provider will likely require this.

Fasting glucose and insulin — Track improvements in insulin sensitivity alongside A1c.

CMP — Monitor kidney and liver function, especially in the first year when doses are being titrated upward.

Lipid panel — Triglycerides often improve quickly (within weeks). LDL and HDL changes take longer.

CBC — Ensure no nutritional deficiencies are developing. Significant caloric restriction can lead to deficiencies in iron, B12, and folate over time.

Vitamin D and B12 — Reduced food intake and changes in absorption can deplete these. B12 deficiency in particular can cause neurological symptoms that are easy to miss.

Thyroid (TSH) — Annual check, or sooner if you develop new symptoms.

Uric acid — If you had elevated levels at baseline or experience joint pain.

One of the most discussed concerns with GLP-1 medications is muscle loss. These drugs suppress appetite dramatically, and if protein intake drops too low, the body can break down muscle alongside fat.

While there's no single blood test that directly measures muscle mass, these markers are useful proxies:

• Creatinine — Can decrease with significant muscle loss (counterintuitively, low creatinine may signal reduced muscle mass in this context)
• Albumin — A marker of protein status; low albumin suggests inadequate protein intake
• BUN (blood urea nitrogen) — Part of the CMP; can reflect protein metabolism

Tracking these alongside body composition measurements (DEXA scan or bioelectrical impedance) gives the most complete picture.

Rapid weight loss significantly increases the risk of gallstones. GLP-1 medications can also affect gallbladder motility. If you develop upper right abdominal pain, nausea after fatty meals, or shoulder pain, a liver function panel and discussion with your provider is warranted.

Once you have your baseline labs, share them with your prescribing provider — whether that's a primary care physician, endocrinologist, or telehealth platform. They'll use these numbers to:

• Confirm you're a good candidate for GLP-1 therapy
• Set a starting dose appropriate for your metabolic status
• Establish monitoring intervals
• Identify any issues that need to be addressed before or during treatment

If you're managing your own protocol through a compounding pharmacy or peptide source, your labs become even more important — they're your primary safety net.

At Reliable Exams, you can order a complete GLP-1 baseline panel or monitoring panel online and walk into any LabCorp or Quest Diagnostics location near you — no appointment, no referral, no waiting room.

Results are typically ready in 1–2 business days, delivered securely to your online account.

Start informed. Stay informed. Your metabolic health is worth tracking.